The present invention relates to a slip clutch mechanism using frictional engaging force, such as a small-sized slip clutch mechanism appropriate for being built, for example, into a camera.
A slip clutch mechanism has hitherto been known in various types of construction. In this regard, it has been necessary to make a spring large in order to produce a large sliding torque in a clutch mechanism which obtains its sliding torque by the use of the force derived from the spring.
The present applicant has developed an apparatus for driving a group of lenses having variable magnifications with a driving motor for zooming. The motor is built into the apparatus for driving the zoom lens and is used as an interchangeable lens for a single lens reflex camera, and is commonly known as a power zoom lens. For the lens barrel for such a power zoom lens, a slip clutch mechanism is indispensable because the variable magnification lens group must be stopped even if the motor continues to rotate when the variable magnification lens group has reached its telescopic end or a wide angle end, and in case an excessive load has been exerted. However, an interchangeable lens has such a limited space that it is difficult to increase the sliding torque by employing a larger spring, which presents the problem that it is not possible to obtain the necessary sliding torque for such a variable magnification lens group, because of the limiting factors such as the weight of the lens group. Also, the conventional slip clutch mechanism is liable to the occurrence of a slip in it in consequence of the dead load of the variable magnification lens group. Thus, it has been desired that these problems inherent in the conventional slip clutch mechanism will be resolved.